The principle objective of this application is to discover novel disease pathways in a Drosophila melanogaster model of amyotrophic lateral sclerosis (ALS). Recently, dominant mutations in the RNA binding protein TDP-43 (43 kDa TAR DNA-binding protein) have been causally linked to ALS. In addition, ubiquitin-positive, insoluble aggregates of TDP-43 are frequently observed in degenerating motor neurons of ALS patients, suggesting that deregulation of TDP-43 through mutation or epigenetically is a precipitating event in this disease. We have generated a fruit-fly model of TDP-43 proteinopathy in which the expression of human TDP-43 in the motor neurons of flies leads to age- dependent paralysis and death. In this model, TDP-43 retains a nuclear expression pattern, suggesting that TDP-43 need not aggregate to cause motor neuron dysfunction. Based on these findings we hypothesized that TDP-43-dependent changes in nuclear gene expression are responsible for neurodegeneration. Consistent with this idea, gene expression analysis of TDP-43 transgenic flies identified deregulation of cellular pathways with plausible links to neurodegeneration. The goal of the present proposal is to use the Drosophila TDP-43 model to gain new insights into TDP-43-dependent neurodegeneration. The grant encompasses two specific aims. In Aim 1 we will perform microarray and RIP-Chip studies to identify TDP-43 RNA targets in motor neurons. In Aim 2 we will perform screens for genetic modifiers of TDP-43-dependent neurodegeneration, using both candidate and unbiased approaches. The combined studies should illuminate mechanisms of neurodegeneration in ALS and related proteinopathies that may lead to new therapeutic options. PUBLIC HEALTH RELEVANCE: ALS is an intractable condition that exerts severe tolls on affected patients, their families, and caregivers. Comprehensive approaches aimed at identifying the operative mechanisms in this disease are urgently needed. We believe that the fruit fly model of ALS to be explored in this proposal will provide important clues regarding ALS pathogenesis that may lead to new therapies.